A new self-organizing mechanism for deep-focus earthquakes

  title={A new self-organizing mechanism for deep-focus earthquakes},
  author={Harry W Green and Pamela Burnley},
THE mechanism of deep-focus earthquakes has been a puzzle since their discovery almost 70 years ago1, 2, because brittle fracture and frictional sliding at depths in excess of 100–200 km would require unrealistic rock strengths3, 4. Rock strength does increase with pressure, but a few hundred MPa (equivalent to 10–20 km depth) suffices to inhibit most fracture, and elevated temperature activates ductile mechanisms that operate at stresses less than the fracture stength. A range of mechanisms… 

The failure mechanism for deep-focus earthquakes

Abstract Experimental deformation of Mg2GeO4 olivine at pressures between 1 and 2 GPa in the spinel stability field has led to discovery of a faulting instability that develops at the

Shearing instabilities accompanying high-pressure phase transformations and the mechanics of deep earthquakes

  • H. Green
  • Geology
    Proceedings of the National Academy of Sciences
  • 2007
Extensive seismological interrogation of the region of the Tonga subduction zone in the southwest Pacific Ocean provides evidence suggesting significant metastable olivine, with implication for its presence in other regions of deep seismicity.

Anticrack-associated faulting at very high pressure in natural olivine

SHALLOW earthquakes are produced by brittle shear fracture of rock and/or fictional sliding on pre-existing fault surfaces1. At very high pressures, however, brittle fracture and frictional sliding

Deep-Focus Earthquake Analogs Recorded at High Pressure and Temperature in the Laboratory

Microstructural observations prove that dynamic weakening likely involves superplasticity of the nanocrystalline spinel reaction product at seismic strain rates, and explores the feasibility of phase transformations of metastable olivine that might trigger deep-focus earthquakes in cold subducting lithosphere.

Fast rise times and the physical mechanism of deep earthquakes

EARTHQUAKES at depths of > 300 km are similar to shallower events in that they are dominantly of double-couple character1, implying that shearing motion has taken place at depth. But because

Mechanisms of deep earthquakes

In most tectonic settings, no earthquakes occur below about 30 km depth. This is because increasing pressure inhibits frictional sliding, whilst increasing temperature promotes ductile deformation.

Mechanism of Deep - Focus Earthquakes Inferred from High Pressure Experiments

Deep-focus earthquakes occur at depths from the earth's surface up to 680 km (corresponding to pressure of 24 GPa). They occur only in the restricted areas in the earth, or the subduction zones.



Localized polymorphic phase transformations in high‐pressure faults and applications to the physical mechanism of deep earthquakes

Earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes. Such mechanisms, in unmodified form, are highly unlikely for deep earthquakes because

Deep‐earthquake initiation by phase transformations

The following mechanism for deep earthquakes is proposed: Due to the relative motion of mantle and plate, material crosses a phase stability line. The new phase, with a different molar volume, is

Earthquakes and faults

Abstract The hypothesis that earthquakes are caused by faulting has been prominent in seismological theory for half a century, but continues to present many difficulties. Although the chief support

Olivine‐spinel transitions: Experimental and thermodynamic constraints and implications for the nature of the 400‐km seismic discontinuity

The sequence of high-pressure phase transitions α→β→γ in olivine is traditionally used as a model for seismic velocity variations in the 200- to 650-km-depth interval in a mantle of peridotitic bulk

Plastic instabilities: Implications for the origin of intermediate and deep focus earthquakes

Adiabatic or catastrophic plastic shear has been reported in metals, polymers, and metallic glasses. The phenomenon is associated with rapid stress drops and audible pings or clicks as the material

Shear instability in a viscoelastic material as the cause of deep focus earthquakes

The mechanism of deep focus earthquakes has been examined by numerical and linear analysis of shear instability in subducting slabs. We assume subducting slabs deform such that the spatially averaged

Stress dependence of the mechanism of the olivine–spinel transformation

OLIVINE, α-(Mg,Fe)2SiO4, is the most abundant phase in the Earth's upper mantle. It transforms to high-density polymorphs (α, with the spinel structure and β, with a modified spinel structure) under

Source wave forms of three earthquakes

Strain seismograms of the Montana shallow earthquake of August 17, 1959 recorded at Isabella, California have the wave pattern predicted in 1904 by Lamb for a surface pressure pulse. This is